Almost all semiconductor components are enclosed in packages when they are incorporated into a working electronic system. Typically, integrated circuits are enclosed in an appropriate package prior to their sale by the integrated circuit manufacturer.
There are many reasons for providing a proper environment around an integrated circuit. For example, appropriate packaging of an integrated circuit generally results in a dramatic economy in assembly. Integrated circuits chips are extremely small and fragile, and therefore are difficult to handle without the aid of magnifying and manipulating equipment. Placement of a chip into an integrated circuit ("IC") package overcomes the difficulty of handling the chip by providing a relatively large and easily handled package configuration. A second important function fulfilled by IC packages is mechanical protection of the chips. Because the integrated circuit chips are generally made from fragile materials, they must be protected from the possibility of scratches and chipping. A third essential function of an IC package is to shield the enclosed integrated circuit chip from the surrounding environment so as to preclude contamination, corrosion and other detrimental effects resulting from exposure to the normal environment.
The drive toward smaller and smaller system size has lead to the expanding development and use of solid state semiconductor devices and is accompanied by a strong need for a satisfactory miniaturized sealed package or enclosure for semiconductor devices. A limiting factor in further size reduction of electronic systems is the size of the IC package itself, which is generally several times the size and weight of the semiconductor device which it houses. Heretofore, difficulties have been encountered in reducing the package size and thickness while continuing to provide adequate means for making electrical connections to the package and for transferring heat from the semiconductor element to an external heat sink. The attainment of a good hermetic seal for the semiconductor element and particularly at the junction between the walls of the enclosure and the leads projecting externally, and providing suitable external connection arrangements to provide versatility and means of making interconnections and for ease of mounting the device on a supporting structure must be maintained in the smaller sized package. The IC package referred to hereinafter may be employed, for example, for encapsulating semiconductors such as diodes, transistors, integrated circuits and complete functional electronic elements.
Electrical devices such as integrated circuits, electroconductive film resistors, transistors, diodes, semiconductors, and the like are commonly sealed in a container or enclosure having a body of electrically insulating or conducting material. Such bodies are formed with a relatively large planar bottom wall surrounded by a rim defining a cavity within which an electrical device is disposed. Leads extending from within the cavity to the outside of the body are provided. The electrical device is typically connected to these leads within the cavity by wirebonding the connector pads to the leads with extremely small and fragile wires. The wirebonded chip assembly is then enclosed within the cavity by a rigid cover plate disposed over the cavity and sealed to the rim. This type of construction has many drawbacks, the magnitude of which increase as the size of the package decreases. For example, the assembly becomes more and more tedious and time consuming, the package becomes more fragile, and the dissipation of heat from the device becomes more difficult.